1. Field of the Invention
The present invention relates to a ramp generation circuit and an A/D converter and is more specifically applied to, e.g., an A/D converter when a ramp wave output from a ramp generation circuit has a small slope.
2. Description of the Related Art
There is conventionally an A/D converter having an output circuit and a converter circuit. The output circuit generates an analog signal and outputs it to the converter circuit as a reference signal. The converter circuit receives the reference signal from the output circuit and outputs a desired digital signal (e.g., Jpn. Pat. Appln. KOKAI Publication No. 2006-81203).
However, the reference signal such as a ramp wave output from the output circuit contains all sorts of noise such as noise from peripheral circuits and noise in the output circuit itself. This degrades the S/N ratio (signal-to-noise ratio) of the reference signal. Even when the slope of the ramp wave of the reference signal changes, the magnitude of noise contained in the ramp wave does not change. For this reason, the smaller the slope of the ramp wave becomes, the more conspicuously the S/N ratio degrades.
Consequently, the output error of the converter circuit that receives the reference signal as the input signal grows. Hence, the output error of the A/D converter also becomes large.
As described above, the conventional ramp generation circuit and A/D converter tend to degrade the S/N ratio and increase the output error.